In order to operate automotive vehicles within mandated exhaust emission limits it is necessary to properly control to a selected air/fuel ratio and that requires a determination of the mass air flow so that the fuel injection rate can be correctly adjusted. In addition to emission concerns, it is desired to obtain fuel consumption efficiency and good engine performance. All of these objectives tax the capabilities of fuel control systems. Rapid time response as well as precision of mass air flow measurement have become high priority goals.
It has been a common practice to measure mass air flow at a fixed time interval. In the event of transients in air flow due to changes in engine operating parameters it is necessary to employ special transient calculations to approximate the real instantaneous airflow. The calculations are time consuming and lacking in accuracy.
It has been proposed to incrementally sample air flow based on engine rotation during an intake valve event. The sampling rate varies with engine speed and thus requires engine speed information and further cannot be optimally matched to the response time of the air flow meter.